1. Field of Invention
The present invention relates to a surface emitting semiconductor laser, a manufacturing method thereof, a light module and a light transmission device including the surface emitting semiconductor laser.
2. Description of Related Art
A surface emitting semiconductor laser has a large amount of potential as a light source for optical communication and optical computing and various kinds of sensors. In the optical communication, a surface emitting semiconductor laser is currently tried to be applied to a light source for the short distance optical communication used with a multi modes fiber. Further, a surface emitting semiconductor laser will be applied as a light source for the long distance optical communication used with a single mode fiber in the future.
A transversal mode is a single mode (zero order fundamental mode), as a characteristic of a light source, which is suitable for a single mode fiber. Therefore, when applying a surface emitting semiconductor laser as a light source using a single mode fiber, a stabilized single mode is required.
As one of methods of obtaining light of a single mode with a surface emitting semiconductor laser, it is known that the current aperture is formed by selective oxidation and light is blocked at the same time of narrowing electric current by the current aperture. For example, in a surface emitting semiconductor laser composed of AlGaAs series, a layer having high composition ratio of aluminum can be formed in a multi-layered film mirror in advance and the side of this layer is oxidized thereafter so as to form the current aperture. This current aperture includes the region where composition ratio of Al remained in the center is high (an aperture) and an outskirt region including aluminum oxide (an oxidation blocking portion) which is formed around the above region. However, according to this method, there is a concern that the effect of blocking light is too large since the difference between a refractive index of the aperture and that of the oxidation-blocking portion is too large. Hence, it is desirable that the radius of the aperture is under 4 μm in order to obtain a stabilized single mode. However, in this case, there is the other concern that an element resistance is increased by restricting an electric current path in addition to deteriorating light emission efficiency.